A spark plug is mounted to, for example, an internal combustion engine or a like combustion apparatus, and is used to ignite an air-fuel mixture in a combustion chamber. Generally, the spark plug includes an insulator having an axial hole; a center electrode inserted into a front end portion of the axial hole of the insulator; a terminal electrode inserted into a rear end portion of the axial hole of the insulator; a metallic shell externally assembled to the insulator; and a ground electrode extending from a front end portion of the metallic shell and forming, in cooperation with the center electrode, a spark discharge gap therebetween.
According to general practice, in order to allow external identification of a product No. or the like of the spark plug, a predetermined identifier is engraved on the metallic shell or printed on the surface of an insulator (refer to, for example, Patent Document 1). However, in the case where a plurality of spark plugs are contained in an array in a case, difficulty is encountered in visually checking the identifiers. In order to allow, even in such a case, easy checking of the identifiers marked on the spark plugs, there is proposed provision of an identifier on the rear end surface of the terminal electrode. Conceivably, an identifier is provided such that the identifier is marked by painting or printing.
Patent Document
    [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. H09-277692